The present invention relates to a low-density abrasive article employing an open, porous, lofty nonwoven web containing a multitude of abrasive particles bonded thereto and particularly to an abrasive article containing fused mullite abrasive particles.
Abrasive articles come in many types, each generally designed for specific applications and no one type providing a universal abrading article for all applications. The various types of abrading articles include, for example, coated abrasive articles, i.e. abrasive particles generally uniformly distributed over and adhered to the surface of a flexible backing; grinding wheels, i.e. abrasive material consolidated together in a mass in the form of a rotatable annulus; and low-density abrasive articles, i.e. open, porous, lofty, nonwoven webs impregnated with adhesive which does not alter the open character of the web and also bonds abrasive particles to the web.
Low-density abrasive articles have enjoyed considerable commercial success as metal, wood, and plastic finishing tools. Low-density abrasive articles typically consist of open, porous, lofty nonwoven webs made of either autogenously bonded continuous undulated interengaged filaments or randomly oriented high strength fibers. The nonwoven webs are impregnated with a binder which adhesively bonds the filaments or fibers of the web together and also adhesively bonds a multitude of abrasive particles to the surface of the filaments or fibers. One very successful commercial embodiment of such an abrasive article is that sold under the trade designation "Clean-N-Strip" by Minnesota Mining and Manufacturing Company of St. Paul, Minn.
Low-density abrasive articles of this type may be prepared by the method disclosed by Fitzer in U.S. Pat. No. 4,227,350. The nonwoven web of Fitzer is comprised of continuous undulated interengaged filaments which are autogenously bonded at points of mutual contact. An adherent binder bonds the filaments together and also bonds a multitude of abrasive particles uniformly distributed throughout the nonwoven web, to the surface of the filaments. The abrasive particles may be of any known abrasive material commonly used in the abrasive art having a particle size from grade 10 to grade 600 and a Mohs hardness from 4 to 10.
Although the commercial success of low-density abrasive articles has been impressive, it is desirable to expand their range of performance. Due to their low cutting rates, low-density abrasive articles have not generally been found useful for the removal of a large amount of material or stock from a workpiece, such as for the removal of stock from a carbon steel workpiece. Heretofore, low-density abrasive articles of the type described in Fitzer have been used primarily for the process of surface conditioning, or cleaning of substrates, such as the removal of oxides from surfaces prior to painting.
Because of their higher cut rate, coated abrasive articles have generally been preferred over low-density abrasive articles for the removal of stock from a workpiece. The use of coated abrasive articles is not without disadvantage, however. For example, the use of coated abrasive articles to abrade a workpiece can result in the generation of a significant amount of heat on the surface of the workpiece. This creates the potential to impart scorch marks on the workpiece, which may have to be removed in a subsequent abrading step. In the process of removing surface coatings from a workpiece, the heat generated by coated abrasive articles may cause the surface coating to soften and to be smeared over the surface of the workpiece. The softened coating may also transfer more easily from the workpiece to the coated abrasive article, causing the coated abrasive article to clog or "load" and resulting in a reduction in its useful life.
It is well known that low-density abrasive articles generate less heat during use than coated abrasive articles, due to their open, porous, lofty nonwoven web which permits a degree of cooling. In order to increase the cut rate of a low-density abrasive article a person skilled in the art might be expected to select large particles of well known abrasive minerals, such as Al.sub.2 O.sub.3 or SiC. It has been observed, however, that when certain abrasive minerals, such as Al.sub.2 O.sub.3, are used to abrade carbon steel workpieces, a maximum cut rate is reached beyond which an increase in abrasive particle size does not substantially increase the cut rate of the low-density abrasive article. In addition, it has been observed that on carbon steel workpieces, certain abrasive minerals, such as SiC, when used in a low-density abrasive are ineffective at producing even a moderate cut rate, regardless of abrasive particle size.
In light of the foregoing, it would be desirable to provide an abrasive article which has a high cut rate on substrates, such as carbon steel, yet retains the properties of a nonwoven abrasive such as the reduced tendency to generate heat on the surface of the workpiece being abraded. Moreover, it is desirable to provide such an article using an inexpensive abrasive mineral.